Possible problem with WAN port on 851W

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Aug 12th, 2009
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Hi all,

I just got a 851W and had some trouble setting it up.

Specifically, when I turn on the WAN port, the LINK like would stay lit even when there is no cable connected to the port (fa4). This seems unusual.

Also, show interface gives me a up/up status. I thought the line protocol would be down unless there a physical link (cable connection) and both end are active?

Anyway, I want to make sure my 851W does not have a bad WAN port. Any pointer in determining the viability of the WAN port will be much appreciated.



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kwillacey Wed, 08/12/2009 - 08:52
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configure an ip address on it and connect it to a laptop or another device check if the interface is up and do a ping.

chialoon Wed, 08/12/2009 - 21:51
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Thanks. I already tried that first.

Two things that are unusual:

1. The "link" light stays lit, even without cable connection.

2. The line protocol is UP even though there is no cable connection.

3. When the port is turned on (no shut) and uplinked to a switch port on my other router, the switch port on the other router showed no link. Yes, the cable is straight-through and it's a good working cable.

Any other thoughts? I am trying to determine whether there is a physical problem with WAN port. Thanks.

andrewswanson Thu, 08/13/2009 - 02:52
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are keepalives enabled on the interface? default is 10 seconds but if disabled can cause interface to appear up.



kwillacey Thu, 08/13/2009 - 05:21
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Andrew made a good point check the keepalives and if it's not off then it might be a hardware issue because if it's not connected it should be up down.

Are there any errors on the 851 interface?

chialoon Fri, 08/14/2009 - 03:01
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Thanks for the tips, guys! The keepalive is set to 10 secs. There is no error on the interface. Is there anyway to diagnose whether the interface is physically bad?

Here's an output for your reference:


FastEthernet4 is up, line protocol is up

Hardware is PQUICC_FEC, address is 0018.1813.cc45 (bia 0018.1813.cc45)

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, 100BaseTX/FX

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output never, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

0 packets input, 0 bytes

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog

0 input packets with dribble condition detected

0 packets output, 0 bytes, 0 underruns

0 output errors, 0 collisions, 2 interface resets

0 babbles, 0 late collision, 0 deferred

chialoon Fri, 08/14/2009 - 03:04
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Oh, btw, this problem persists even when I do a hard reset...

kwillacey Fri, 08/14/2009 - 05:52
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i am only familiar with loopback tests for serial interfaces so i'm not sure about the ethernet interface but it seems like a hardware issue, TAC can probably tell you what to do.

chialoon88 Fri, 08/14/2009 - 10:36
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Thanks for your input. Just thought there might be a trick to this.

BTW, just for your reference:

1. Straight-through cable connecting WAN port (Fa4) to another switch showed no activity on the other switch (the switch did not show the link as up). On 851, the LINK light stays steady green.

2. Straight-through connecting WAN port to 851's own switchport (say, Fa0), the switchport shows UP.

I'll need to go back to studying the Ethernet pinouts...

kwillacey Fri, 08/14/2009 - 10:43
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the type of cable (cross over or straight) should not matter since all of the new devices have auto mdix. also given that the switchports work and the routed port i would think something is definitely wrong with that port.

jimmysands73_2 Fri, 08/14/2009 - 17:34
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I am just curious, what happens when you put the port into a shutdown state?

chialoon Fri, 08/14/2009 - 20:18
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The shutdown state is like it should be. The light goes off and the interface is administratively down.


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